Propofol (2,6-Diisopropylphenol) is a well-known and widely used intravenous anesthetic agent. For example, in intensive care units (ICU) where the duration of treatment may be lengthy, propofol has the advantage of a rapid onset after infusion or bolus injection plus a very short recovery period of several minutes, instead of hours.
Propofol is a hydrophobic, water-insoluble oil. To overcome the solubility problem, it must be incorporated with solubilizing agents, surfactants, solvents, or an oil in water emulsion. There are a number of known propofol formulations, such as disclosed in U.S. Pat. Nos. 4,056,635, 4,452,817 and 4,798,846 all of which are issued to Glen and James.
Propofol compositions have been the subject of several patents. Typically, propofol compositions comprise 1-2% by weight propofol, 1-3% or 10-30% of a water immiscible solvent such as soybean oil, 1.2% of egg lecithin as a surfactant, and 2.25% glycerin as a tonicity agent. Variation in pH and/or addition of other components allows for various advantages and uses. For example, Hendler (U.S. Pat. No. 6,362,234) uses propofol esters (100 mg-3 gm) in combination with anti-migraines to make aqueous, solid and other non-aqueous compositions for internal and transdermal delivery, for the treatment of migraines. De Tommaso (U.S. Pat. No. 6,326,406) discloses a composition of pH 4.5-6.5 comprising 10 mg/ml propofol, 25-150 mg/ml bile salt, a lecithin, and preparation with substantially no oxygen. Mixing propofol with bile acid produces a clear formulation and allows for easy detection of foreign particles. For veterinary applications, benzyl alcohol and phospholipid free composition comprising from 1-30% by weight propofol, wherein the aqueous solution is sterile filtered has been used to anesthetize animals (Carpenter, U.S. Pat. No. 6,150,423). Higher percentages of propofol allow for administration of smaller quantities.
To prevent microbial growth, various components and methods of preparation have been discussed. For example, Mirejovsky, et al., disclose compositions of pH 4.5-6.4 with less than 1% sulfites and 1-2% by weight propofol (U.S. Pat. Nos. 6,469,069 and 6,147,122); George, et al., disclose 0.15-0.25% tromethamine with 1-2% by weight propofol and pH 8.5-10 (U.S. Pat. No. 6,177,477); 0.005% EDTA with 1-2% by weight propofol and pH 6-8.5 has been used by Jones, et al., (U.S. Pat. Nos. 5,714,520, 5,731,355, and 5,731,356); George (U.S. Pat. No. 6,028,108), discloses compositions with 0.005-0.1% pentetat that are 1-2% by weight propofol and pH 6.5-9.5. Likewise, lowering pH ranges (pH 5-7), using egg lecithin (0.2-1%) and soybean oil (1-3%), without preservatives and 0.1-6% propofol by weight (Zhang, et al., U.S. Pat. No. 6,399,087), and lowering concentrations of soybean oil (1-3%) to produce stable emulsions and reducing nutrients with 1% propofol by weight (Pejaver, et al., U.S. Pat. No. 6,100,302), are said to provide protection against microbial contamination. Reducing lipid concentrations also reduces the chances of fat overload and is ideal for use when administered over extended time periods. In addition, compositions devoid of fats and triglycerides, with 3% w/v propofol (Haynes, U.S. Pat. No. 5,637,625) are said to be useful for sedation over extended periods of time.
There are two major problems associated with the formulations described in the above patents: (1) the risk of microbial contamination due to the high nutrient content and lack of antimicrobial preservatives. Studies by Arduino, et al., 1991; Sosis & Braverman, 1993; and PDR, 1995, have shown that a propofol emulsion formulated without preservatives will grow bacteria and present a risk of bacterial contamination; (2) Hyperlipidemia in patients undergoing long-term ICU sedation due to a large amount of fat content. Studies have shown that triglyceride overload can become a significant problem when a 1% propofol/10% soybean oil emulsion is used as the sole sedative for a long period of ICU sedation by Gottardis, et al., 1989; DeSoreruer, et al., 1990; Lindholm, 1992; and Eddieston, et al, 1991.
To solve the problem of bacterial contamination of propofol emulsion, the following patented formulations of propofol have been developed:
Patent No.InventorIssued5,637,625Duncan H. Haynes10 Jun. 19975,714,520Christopher B. J., et al.  3 Feb. 19986,028,108Mary M. G.22 Feb. 20006,100,302Satish K. P., et al. 8 Aug. 2000PCT 99/39696Mirejovsky D., et al.12 Aug. 1999PCT 00/24376Mary T., et al. 4 May 2000
The formulations described in U.S. Pat. No. 5,714,520 is sold as DIPRIVAN® and comprises a sterile, pyrogen-free emulsion containing 1% (W/v) propofol in 10% (w/v) soybean oil. The formulation also contains 1.2% (w/v) egg lecithin as a surfactant, 2.25% (w/v) glycerol to make the formulation isotonic, sodium hydroxide to adjust the pH, and EDTA 0.0055% (w/v) as a preservative. This formulation prevents no more than a 10-fold increase against gram negative (such as Pseudomonas aeruginosa and Escherichia coli) and gram positive (Staphylococcus aureus) bacteria, as well as yeast (such as Candida albicans) over a twenty-four hour period. However, EDTA, which is a metal ion chelator, removes cations like calcium magnesium and zinc. This can be potentially dangerous to some patients with low calcium or other low cation levels, and especially critical for ICU patients.
In U.S. Pat. No. 6,028,108 the propofol formulation contains pentetate 0.0005% (w/v) as a preservative to prevent microbial contamination. Pentetate is a metal ion chelator similar to EDTA and therefore represents the same potential danger.
The formulation described in W.O. Patent No. 99/39696, is generic propofol containing 0.25 mg/mL sodium metabisulfite as a preservative to prevent microbial growth. At 24 hours there is no more than a one log increase. Recently, P. Langevin, 1999, has expressed concern that generic propofol containing 0.25 mg/mL sodium metabisulfite, infused at a rate of 50 ug/kg/min, will result in sulfite administration approaching the toxic level (i.e., near the LD50 for rats) in about 25 hours.
Particularly, the addition of sulphites to this drug is worrisome for the potential effects to the pediatric population and for sulphur allergy to the general population. In a June 2000 letter, the manufacturer of metabisulphite-containing propofol emulsion (Gensia Sicor) stated that discoloration and a reduction in pH occur when the product is exposed to air and that both phenomena are caused by the oxidation of sodium metabisulphite Mirejovsky D. Ghosh M. Reply. (Pharmaceutical and antimicrobial differences between propofol emulsion products) (Am J Health-Syst Pharm. 2000: 57:1176-7). Results show that the yellowing of the commercial metabisulphite-containing propofol emulsion is an oxidized form of propofol dimer quinine which is lipid soluble. (U.S. Pat. No. 6,399,087). Recent data also support pro-oxidant activity by the sulfite anion resulting in propofol dimerization and lipid peroxidation (Baker et al., Anesthesiology, 96, A472, 2002).
The formulation described in PCT W.O. Patent No. 00/24376 is a formulation having an antimicrobial agent, which is a member selected from the group consisting of benzyl alcohol and sodium ethylenediamine tetraacetate, benzethonium chloride; and benzyl alcohol and sodium benzoate. The formulation contains EDTA, which was mentioned as related to the side effect above. Benzyl alcohol is linked to adverse reactions reported by Evens and Lopez-Herce, et al. The formulation may be unsafe upon administration, particularly to those patients who need an extended period of ICU sedation.
The formulation described in U.S. Pat. No. 5,637,625 is of phospholipid-coated microdroplets of propofol, containing 6.8% propofol with no soybean oil. However, it is believed that this formulation may increase injection site pain to an unacceptable level during administration.
The formulation described in U.S. Pat. No. 6,100,302 is an emulsion of propofol that contains 1-3% of soybean oil to prevent against accidental microbial contamination during long-term IV infusions due to an increased availability of propofol.
Egg lecithin is mainly used in pharmaceutical products as a dispersing, emulsifying, and stabilizing agent. The lecithin is also used as component of enteral and paranteral nutrition formulations, Arthur H. Kibbe, 2000.
It has been also found that in this invention a propofol formulation containing a reduced amount of egg lecithin results in a significant increase in the ability to be antimicrobial. The soybean oil is also source of nutrition to support the microbial growth.
Thus, it has been found that the preservative-free, optimized propofol formulation of this invention addresses the prior art problems to the point where the problems are eliminated or at the least are substantially reduced.
It has now been discovered that the propofol in propofol formulations with reduced oil content is degraded when stored in a container with a closure that is not inert to propofol. The problem of propofol degradation encountered was quite unexpected as closures sealed with a rubber stopper or the like are known. For example, U.S. Pat. No. 6,576,245 points out that primary packages such as vials, bottles, cartridges, prefilled syringes and the like are typically sealed by a rubber stopper or plunger. U.S. Pat. No. 6,576,245 further expresses a preference for a rubber material containing bromobutyl instead of chlorobutyl to improve the stability of low molecular weight thrombin inhibitors in solution. Heretofore, however, the art has not understood that the propofol in propofol formulations is susceptible to degradation due to exposure to the closure for the container. The failure of the art to recognize the effect of the container closure on propofol degradation, it is believed, is due to the fact that the commercially available propofol formulation DIPRIVAN® comprises 10% (w/v) soybean oil. Applicants have found that at the relatively high volume of soybean oil used in prior art formulations, the soybean oil apparently protects propofol from degradation. However, at oil contents (and/or propofol solvent contents) lower than about 10% (w/v), degradation of propofol has been found to occur if the container closure is not inert or non-reactive to propofol.